Control device and method for automatic transmission

ABSTRACT

In an attempt to accomplish an object to absorb a driving torque difference caused by a difference in a change gear ratio between before and after shifting and to reduce a shift shock, adopted is such a constitution that target driving torque characteristics with which said driving torque before and after shifting will become nearly equal are stored, and engine torque control will be effected according to said characteristics. The control device is so constituted that, during shifting, the engine torque is decreased to suppress a driving torque variation resulting from inertia variation, and the engine torque before a specific period from the completion of shifting is outputted higher than the normal torque, and the engine torque before a specific period from the completion of shifting is outputted higher than the normal torque to reset to the normal engine torque after the specific period after the completion of shifting.

BACKGROUND OF THE INVENTION

The present invention relates to a device for reducing a shift shockwhich is likely to occur when gear shifting is made by an automatictransmission of a car.

It has been a known practice to reduce a shift shock during an upshiftof a car by decreasing an engine torque during shifting through thecontrol of an ignition timing or a quantity of fuel injection forpurpose of diminishing a difference in an inertia energy caused by adifference of engine speed between before and after shifting as statedin the specification of Japanese Patent Application No. 4-63138pertaining to an application of the present patent applicant.

However, in gear shifting occurring during acceleration with the depthof depression of an accelerator pedal unchanged, that is, in a so-calledautomatic upshift, a gear ratio (engine speed/output shaft speed) afterthe shift becomes low; therefore a torque produced in the drive shaftvaries step by step if the engine speed remains unchanging. To absorbthis absolute torque change after shifting is made for the purpose ofdecreasing a shock at the time of shifting in order to insure smoothspeed change, it is imperative to reduce the engine torque substantiallyduring a short period of time. However, in such a construction that theengine torque is transmitted to the driving shaft side through a torqueconverter as in an automatic transmission, the engine torque can not betransmitted to the driving shaft side if the engine speed is not kept atsome level. Here, the engine speed after upshifting lowers according toa gear ratio; therefore when a shock during shifting is lessened bydecreasing the engine torque, there exists such a problem that if theengine torque is decreased excessively, the rate of decrease of theengine speed is accelerated to result in an engine speed drop after thecompletion of in a the shift, and driving torque drop after shifting anda lowered effect of shock reduction.

The present invention has been accomplished in an attempt to solve theaforementioned problem and has as its object the provision of a deviceand method for controlling an automatic transmission which is capable ofeliminating a torque difference between before and after shifting,suppressing inertia variation during a shift, and further insuringdriving safety without deteriorating operation performance even in theevent of a sensor trouble.

To accomplish the aforementioned object, the control device pertainingto the present invention basically has a control means for controllingan engine torque and a transmission control means for controlling anautomatic transmission; the control device comprising a means for nearlyequivalently setting a driving torque immediately before starting ashift and a driving torque immediately after completion of the shift,and a means for suppressing a torque variation during gear shifting.

As a more concrete example, the control device has the control means forcontrolling the engine torque, the transmission control means forcontrolling the automatic transmission, and a means for reducing theengine torque during gear shifting, for the purpose of lessening a shiftshock; the control device comprising a means for increasing the enginetorque during a specific period before the completion of shifting than acommon engine and further for resetting the engine torque, torque aftera specific period after the completion of shifting to a common output.

Furthermore, the control device has the control means for controllingthe engine torque, the transmission control means for controlling theautomatic transmission, and the means for decreasing the engine torqueduring shifting, thereby lessening a shift shock; the control devicecomprising the means for nearly equivalently setting the driving torqueimmediately before the starting of shifting and the driving torqueimmediately after the completion of shifting, and a means for increasingthe engine torque from a specific period before the completion ofshifting than the common engine torque, and for resetting the enginetorque after a specific period after the completion of shifting to acommon output.

Furthermore, as a control means for controlling the engine torque, forexample an electronic throttle valve or a large-capacity idle speedcontrol valve and so forth may be used.

The engine torque at which the driving torques before and after shiftingwill become nearly equal is estimated from the gear ratio before andafter shifting and characteristics of the torque converter, giving theengine the quantity of intake air occurring at this engine torque.During shifting, the quantity of intake air is decreased in accordancewith a shift command signal and turbine rotation on the output side ofthe torque converter, thereby reducing the engine torque for the purposeof suppressing a driving torque variation by an inertia change.Furthermore, during the specific period before the completion ofshifting, the amount of intake air is increased more than during aperiod of normal operation, thus lowering the rate of decrease in theengine speed in order increase to the engine torque. At the same time,the amount of intake air is reset to that during normal operation afterthe specific period after the completion of shifting, to prevent thedrop of the engine speed after shifting, thereby restraining the drop ofthe torque converter output immediately before the shifting andrealizing smooth shifting.

Other objects and features of the present invention will become apparentfrom the embodiment described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing first embodiment of thesystem of a control device according to the present invention;

FIG. 2 is a characteristic drawing of driving torque having no stepbetween before and after shifting;

FIG. 3 is one example of a characteristic drawing of a torque converter;

FIG. 4 is one example of a torque characteristic drawing of an engine;

FIG. 5 is a block diagram showing the constitution of an engine controlunit;

FIG. 6 is a bloc diagram showing the logic of shift shock reduction;

FIG. 7 is one example of an ignition timing map;

FIG. 8 is a view showing the time variation of the characteristics inthe first embodiment;

FIG. 9 is a block diagram showing a control system in the secondembodiment of the present invention;

FIG. 10 is a driving torque characteristic view;

FIG. 11 is a characteristic view of engine torque for shock reductioncontrol; and

FIG. 12 is a view showing the time variation of characteristics in thesecond embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter each embodiment of an automatic transmission control deviceand method according to the present invention with reference to theaccompanying drawings. It should be noted that the same members aredesignated by the same reference numerals and will not be described inorder to prevent redundancy.

First, a first embodiment of a control device according to the presentinvention will be explained by referring to FIGS. 1 to 8.

FIG. 1 is a block diagram showing the outline of the whole system of thecontrol device of the present invention. In FIG. 1, the control deviceis primarily composed of an electronic throttle 8 for controlling theamount of intake air of an engine 11, an engine control unit 10, atransmission control device an accelerator opening sensor 15, a carspeed sensor 14 mounted in a transmission 12, a transmission input shaftspeed sensor 16, and an engine speed sensor 17.

The engine control section 10 is composed of a target driving torquecomputing section 1 for calculating out a target driving torque inaccordance with car speed and accelerator opening, a transmission inputshaft torque computing section 2 for converting the target drivingtorque to a torque of a transmission input shaft 13, a target enginetorque computing section 3, a torque computing section 5 for lesseningshift shock, a throttle opening computing section 4, and fuel injectionand ignition control section 6 for computing and controlling fuel andignition timing.

In the target driving shaft torque computing section 1 a target drivingshaft torque map according to the car speed and accelerator opening asshown in FIG. 2 has been stored. Here, for the target driving shafttorque map is set a characteristic so that the driving shaft torquebefore and after shifting will be equal. That is, an increase anddecrease in the engine torque is controlled by means of the electronicthrottle 8 in relation to a fixed engine torque, to thereby reduce achange in the driving torque which results from a difference in a changegear ratio, thus eliminating a step in the driving torque between beforeand after shifting. For example, if there still occurs a step in thedriving torque at a maximum engine torque output at shift point, shiftcurves of a transmission control unit 7 will be changed in accordancewith a command outputted from the engine control unit 10.

In the engine torque computing section 3 the characteristics curves ofthe torque converter 9 as shown in FIG. 3 have previously been stored;and in the throttle opening computing section 4 the torquecharacteristics curves of the engine 11 as shown in FIG. 4 havepreviously been stored.

The constitution of the driving power control device has heretofore beendescribed; the actual constitution of a hardware of the engine controlunit 10, as shown in FIG. 5, comprises an input interface circuit 20, aCPU 21 which executes various computations, ROM 22 and RAM23 for storingvarious data and programs, and an output interface circuit 24.

Mapped data such as engine characteristics curves, and an operationprogram which realizes the present invention, have been stored inmemory; the CPU21 executes operation in accordance with the operationprogram stored in the ROM22 while inputting and outputting data in theprocess of operation by using data from the input interface 20 and theROM 22. A result of this operation is outputted to the output interfacecircuit 24, thus accomplishing the above-described functions.

Next, the function of the control device of the above-describedconstitution will be explained.

The target driving torque computing section 1 retrieves the targetdriving torque map of FIG. 2 from the accelerator opening and the carspeed, calculating out the target driving torque required. The torquemap has been set to equalize the driving torque before and aftershifting as described above.

The torque computing section 5 for reducing a shift shock serves tosuppress driving torque variation resulting from the inertia of theengine and the transmission during shifting; the current driving torqueis calculated out from speed information fed from the transmission inputshaft sensor 16 and speed information fed from the engine speed sensor17 to gain a difference from the target driving torque previouslystated, and gives this calculated value and the target driving torquewith a portion of inertia taken into consideration from the aforesaidtarget driving torque, to the transmission input shaft torque computingsection 2.

Next, the block diagram of the torque computing section 5 for lesseninga shift shock will be explained by referring to FIG. 6. First, thetransmission input shaft torque will be calculated by using the enginespeed and the transmission input shaft speed. A value as thus calculatedvaries largely and is inadequate for use as a control parameter, andtherefore it is necessary to smoothen a signal by a filter. Start ofcomputation of the torque for lessening a shift shock is judged on thebasis of a specific timing determined from the amount of variation ofthis signal and a shift command signal fed from the transmission controlunit 7. When no torque calculation is effected, the amount of correctionof the target driving torque will be set to zero and no correction willbe made. After starting the torque calculation, the current drivingtorque Tn will be computed from the calculated torque and change gearratio after filtering and the throttle opening, computing a differencefrom the output Tt of the target driving torque computing section 1. Avalue thus obtained will be used as the output Ti of the torquecomputing section 5 for lessening the shift shock.

The transmission input shaft torque computing section 2 calculates outthe transmission input shaft torque by the use of a change gear ratiofed from the transmission control device 7, in relation to a valuegained by adding the calculated value of torque Ti for lessening theshift shock to the target driving torque Tt previously stated.

Furthermore, the target engine torque computing section 3 calculates outa target engine speed and a target engine torque by using the torqueconverter characteristics on the basis of the transmission input shafttorque.

The torque converter 9, as known well, functions to amplify the torquebecause of slip occurring between a pump and a turbine. It is,therefore, necessary to obtain a target engine torque from a rate oftorque amplification and at the same time to calculate out the targetengine speed by correcting the slip. Generally, the torque convertercharacteristics, as shown in FIG. 3, an input/output speed ratio e=n1/n2is plotted on the horizontal axis and a torque ratio between input andoutput t=T/T2 and a capacity coefficient Cp=T1/n1 are plotted on thevertical axis, where n1 is an input speed (engine speed), n2 is anoutput speed (transmission input speed), T1 is an input torque (enginetorque), and T2 is an output torque (transmission input shaft torque).The capacity coefficient Cp expresses the characteristics of the torqueconverter, which are determined in accordance with the size andconstruction of the torque converter. Here, the capacity coefficient Cpis expressed by the input torque T1 and the input speed n1; the capacitycoefficient Cp' can be expressed, using the output torque T2 and theoutput speed n2 as follows:

    Cp'=T2/n22=tCp/e2                                          (1)

Then, using T2 for the target transmission input torque and n2 for thetransmission input shaft speed, the capacity coefficient Cp' isdetermined from Equation 1. The transmission input shaft speed n2 isdetermined from the driving shaft speed fed from the car speed sensor 14and the change gear ratio. When the capacity coefficient Cp' isdetermined, the speed ratio e and the torque ratio t are determined fromthe torque converter characteristics shown in FIG. 3, thence gaining thetarget engine torque and the target engine speed. Here, no dueconsideration is given to such factors as the temperature of the torqueconverter oil, but in actual control it is desirable to correct thevariation of the torque converter characteristics caused by oiltemperature change.

The throttle opening computing section 4 functions to compute thethrottle opening from the engine characteristics previously stored asshown in FIG. 4, and the target engine torque and target engine speeddetermined by the engine torque computing section 3. Also, if a sensorfor obtaining information for determining the target engine torque orthe target engine speed is faulty, and if the target engine torque orthe target engine speed can not be obtained by using other information,and further the faulty sensor is other than the accelerator openingsensor 15, the throttle opening will be calculated out in accordancewith the accelerator opening-throttle opening curves previously set inthe throttle opening computing section 4, thereby enabling to easilyrealize fail-safe operation in the event of a sensor trouble.

At the fuel injection and ignition timing control section 6, control isexecuted to set an optimum fuel and ignition timing according to thepreset throttle opening, thus obtaining the target driving shaft torque.Previously stored in this fuel injection and ignition timing controlsection 6 is a map showing the optimum spark advance angle with thebasic quantity of fuel injection TP and the engine speed as parametersas shown in FIG. 7. If the throttle valve opening changes and the basicquantity of fuel injection TP has changed from the point a to the pointb in FIG. 7, the engine speed hardly rises immediately after a change ofthe throttle valve opening. And the corresponding ignition timingchanges from ar to br. Thereafter the ignition timing changes to cr withthe increase of the engine speed, thereby calculating out the optimumignition timing. For the quantity of fuel to be injected, a similar mapis prepared for the selection of the optimum quantity of fuel throughthe aforesaid step.

In FIG. 8 is shown a relationship between the movement of the throttleduring an upshift and the driving torque in the present embodiment. Abroken line indicates the behavior of throttle and driving torque whenno correction by the throttle is effected, while a full line indicatesthe behavior thereof after correction by the present invention.

In the present embodiment, the throttle is designed to open wider aftershifting than before shifting so as to correct a driving torquedifference between before and after shifting which occurs due todifference in the change gear ratio. That is, during shifting isdecreased a shift shock in the inertia phase in which the correction ofthrottle opening by the shock reducing torque computing section 5 works.By this operation the driving torques before and after shifting willagree, thereby eliminating a torque difference after shifting which willbecome a factor of the shift shock in order to allow smooth speedchanges.

Next, a second embodiment of the present invention will be explained.

FIG. 9 is a block diagram showing the outline of system of the controldevice pertaining to the second embodiment. Only a difference betweenthe present embodiment and the illustrated example in FIG. 1 is presentin the location where the torque computing section for reducing a shiftshock acts. Hereinafter, therefore, an explanation will be made with animportance placed on this difference.

According to the target driving torque map set in the target drivingtorque computing section 1, there occurs a torque difference duringshifting as in a conventional car as shown in FIG. 10.

Furthermore, in the shock reducing logic section 5, the change gearratio is calculated from the transmission input shaft speed and theengine speed, and the torque reduction characteristics in relation toeach shifting will be selected according to a shift position signal fedfrom the transmission control unit 7. The characteristics curve selectedis restricted by a function of the change gear ratio as shown in FIG.11, wherein nS is a change gear ratio at a shift starting point; nEindicates a change gear ratio at the shift end point; and n1 to n3 arecontrol changeover points.

In FIG. 11, when gear shifting starts, the shock correction datagradually decreases to 50% from a point where the change gear ratiobecomes n1, and rapidly increases to 150% from the change gear ratio n2.Then, at the point of n3, this multiplier is held until the point nTwhere the transmission input shaft speed reverses to positive or zero;after this reversion, the shock correction data decreases to 100% in afixed time. At this time the gears are already in engagement, and so ifthe throttle is left open for a prolonged duration, the car will startautomatically. To prevent this, the speed during a period of throttleclosing changes at a higher rate than the speed at which the multiplierdecreases from the point of n1.

FIG. 12 shows a behavior of the present embodiment of the controldevice, in which the throttle opening starts lowering from n1 and turnsupwardly at n2; at n3 the throttle opening, after holding its value,returns to a normal opening. The broke line indicates its movementduring normal operation, from which it is understood that a torque dropat the end of shifting as appearing with the driving torque can beprevented, thereby lessening a shift shock.

The output of the shock reducing logic section 5 is multiplied to thetarget throttle opening calculated out by the throttle opening computingsection 4. That is, up to n1 the output of the throttle openingcomputing section 4 itself (100%) is outputted and thereafter thethrottle opening is so controlled as to vary at a specified rate asshown in FIG. 11.

The embodiments of the present invention have heretofore been describedin detail. It should be noted, however, that the present invention isnot limited only thereto but various changes in design are possiblewithin the scope of the present invention.

For example, the engine torque is controlled by the throttle in each ofthe above-described embodiments, but a large-capacity ISC (Idle SpeedControl) valve may be used in place of the throttle to realize theseembodiments. Also, the first embodiment can be realized by decreasingthe quantity of fuel before shifting and increasing the quantity of fuelafter shifting.

Furthermore it is apparent that a better multiplier effect can beobtained by combining the first and second embodiments.

According to the control device of the automatic transmission of thepresent invention, as is understood from the above description, it ispossible to eliminate a torque difference between before and aftershifting and to suppress an inertia variation during shifting, andtherefore the driver will hardly feed a torque variation duringshifting. Also, even when a sensor trouble is encountered, a shift canbe made to the same control as conventional one and therefore drivingsafety is insured without impairing operation performance.

What is claimed is:
 1. A control device for an automatic transmissionhaving a control means for controlling an engine torque and atransmission control means for controlling said automatic transmission,said control device utilizing a targeted engine torque as a function ofa targeted driving torque and a torque converter characteristic, andcomprising: a means for setting a driving torque immediately beforestarting shifting and a driving torque immediately after the completionof shifting at a nearly equal value, and a means for restraining torquevariation during shifting.
 2. A control device for an automatictransmission according to claim 1, wherein said control means forcontrolling said engine torque is an electronically controlled throttlevalve.
 3. A control device for an automatic transmission according toclaim 1, wherein said control means for controlling said engine torqueis a large-capacity idle speed control valve.
 4. A control device for anautomatic transmission having a control means for controlling an enginetorque, a transmission control means for controlling an automatictransmission, and a means for decreasing said engine torque duringshifting to reduce a shift shock, said control device utilizing atargeted engine torque as a function of a targeted driving torque and atorque converter characteristic, and comprising: a means for increasingsaid engine torque for a specific period before the completion ofshifting greater than normal engine torque, and for resetting to anormal output said engine torque after a specific period after thecompletion of shifting.
 5. A control device for an automatictransmission according to claim 4, wherein said control means forcontrolling said engine torque is an electronic throttle valve.
 6. Acontrol device for an automatic transmission according to claim 4,wherein said control means for controlling said engine torque is alarge-capacity idle control valve.
 7. A control device for an automatictransmission having a control means for controlling an engine torque, atransmission control means for controlling an automatic transmission,and a means for reducing an engine torque during shifting, said controldevice utilizing a targeted engine torque as a function of a targeteddriving torque and a torque converter characteristic, and comprising: ameans for setting a driving torque immediately before the start ofshifting an a driving torque immediately after the completion ofshifting to a nearly equal value, and a means for increasing said enginetorque for a specific period before the completion of shifting greaterthan a normal engine torque, and for resetting said engine torque aftera specific period after the completion of shifting to a normal output.8. A control method for controlling an engine torque and operation of anautomatic transmission, comprising the steps of setting a driving torqueimmediately before the start of shifting and a driving torqueimmediately after the completion of shifting to a nearly equal valuebased on a targeted engine torque as a function of a targeted drivingtorque and a torque converter characteristic, and restraining torquevariation during shifting.
 9. A control method for an automatictransmission according to claim 8, wherein said engine torque iscontrolled by an electronically controlled throttle valve.
 10. A controlmethod for an automatic transmission according to claim 8, wherein saidengine torque is controlled by a large-capacity idle speed controlvalve.
 11. A control method for an automatic transmission for reducing ashift shock comprising the steps of controlling an engine torque byutilizing a targeted engine torque as a function of targeted drivingtorque and a torque converter characteristic, controlling operation ofsaid automatic transmission, and deceasing said engine torque duringshifting, increasing said engine torque for specific period before thecompletion of shifting greater than a normal engine torque, andresetting said engine torque after a specific period after thecompletion of shifting to a normal output.
 12. A control method for anautomatic transmission according to claim 11, wherein said engine torqueis controlled by an electronically controlled throttle valve.
 13. Acontrol method for an automatic transmission according to claim 11,wherein said engine torque is controlled by a large-capacity idlecontrol valve.
 14. A control method for an automatic transmission,comprising the steps of controlling an engine torque utilizing atargeted engine torque as a function of targeted driving torque and atorque converter characteristic, controlling operation of said automatictransmission, and for decreasing said engine torque during shifting forthe purpose of reducing a shift shock, setting a driving torqueimmediately before the start of shifting and a driving torqueimmediately after the completion of shifting, increasing said enginetorque for a specific period before the completion of shifting greaterthan a normal engine torque, and resetting said engine torque after aspecific period upon completion of shifting to a normal output.